Ok guys.
In the winter time or cooler weather, the humidity from out exhaled breath( consistes of lot of water vapor) quickly condenses to the wall of glass because the glass is cooler than the body temp.
In summer it takes longer to fog up as the glass is not that cold.

When you turn the defrost on, the AC compressor kicks in and the air in the cabin is dehumidified no matter where you set the temp dial. This principle is true for all the cars.

In MB setting to defrost kicks on AC compressor and automatically overrides the temp dial setting and sends warm air from defrost vents.

MVK

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1985 300D Turbo 179,000miles